Method and System for Injecting Low Pressure Oxygen from an Ion Transport Membrane into an Ambient or Super Ambient Pressure Oxygen-Consuming Process

ABSTRACT

A stream of sub ambient oxygen from an ion transport membrane is injected into an ambient pressure or super ambient pressure oxygen-consuming process through an annular space in between concentrically disposed inner and outer tubes where a high velocity gas is injected into the process from the inner tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

BACKGROUND

1. Field of the Invention

The present invention relates to injection of oxygen from ion transport membranes.

2. Related Art

Oxy-Combustion in Glass Manufacturing Process

Air-fired glass melting furnaces has been converted to oxygen-fired technology (i.e., oxy-combustion with oxygen concentrations in the oxidant of up to 100%) primarily due to environmental regulations. Oxy-combustion is one of the most thermally efficient and cost-effective ways to enable glass manufacturers to meet NOx emissions restrictions. Compared with air-fired combustion, oxy-combustion has the potential to reduce NOx emissions by up to 85%.

Besides the reduction of NOx emissions, the oxy-combustion has several other significant advantages over traditional air-fired combustion processes:

-   -   the mass and volume of the flue gas are reduced by ˜75%;     -   there is less heat loss in the flue gas due to the reduction of         the flue gas volume;     -   the size of the flue gas treatment equipment can be         significantly reduced     -   the flue gas is primarily CO₂, which is suitable for         sequestration;     -   the separation of pollutants from CO₂ is easier since the         concentration of pollutants in the flue gas is higher than that         produced by air-fired combustion;     -   most of the flue gas is condensable, which makes compression         separation an option;     -   the heat of condensation can be captured and reused.

However, economically speaking, oxygen (for use in oxy-fuel combustion) is costly for glass melting furnaces. The main cost increase is the separation of oxygen from air using a cryogenic air separation unit (ASU). This separation process requires a great deal of energy. For example, in the field of power generation nearly 15% of the production of a coal-fired power station can be consumed by the ASU.

Thus, there is a need for an alternative method of producing O₂ at relatively low cost for use in oxy-combustion technology by the glass industry.

Nevertheless, oxygen generated at high temperatures has the potential to benefit oxy-combustion processes by reducing the amount of fuel needed. In comparison to ambient temperature oxy-combustion, it has been demonstrated that as much as 10% of the fuel requirement may be reduced if the oxygen is preheated to 550° C. and the natural gas fuel is preheated to 450° C. Preheating O₂ to a higher temperature could provide an even greater reduction of the fuel requirement. However, handling pure O₂ at a temperature higher than 650° C. is very difficult and there are very few materials that have been shown to reliably withstand such high temperatures in the O₂ rich environment.

Ion Transport Membranes

Ion transport membranes (ITMs) are fabricated from ionic and mixed-conducting ceramic oxides that conduct oxygen ions at elevated temperatures of 800-900° C. There are a wide variety of materials that are suitable for use in ITMs and their details need not be duplicated herein.

ITMs are considered desirable for integration with glass melting furnaces. Because the glass melting furnace flue gas temperature is roughly 1400° C. at the exit of the combustion chamber, the thermal energy of the hot flue gas can be partly recovered through heat transfer with compressed air, which in turn is used as the feed gas for the ITM. In operation, air is typically compressed to about 16 bars, heated to 900° C., and fed to the ITM. Hot oxygen permeates through the ITM. In order to provide a suitable driving force across the membrane, the oxygen partial pressure of the permeate must be kept low. Typically, an oxygen recovery of 50% to 80% from air is potentially possible. While the O₂ product is available at 900° C., its pressure depends upon the degree of recovery from the air feed gas. The O₂ product may be available at a desirably high pressure of about 2.2 bar, but at the expense of relatively low recoveries. At relatively higher recoveries, the O₂ product may only be available at pressures as low as about 0.5 bar.

Glass melting furnaces operate at high temperatures and at pressures a few Pascal above the ambient pressure. O₂ recovered at high temperature and at a relatively high pressure (i.e., >1.1 bar) from an ITM does not require further preheating and is suitable for injection into the glass melting furnace (via a lance or burner). If greater recoveries are desired, the resultant O₂ is generated at pressures below ambient. There are difficulties experienced when attempting to inject such low pressure O₂ into the furnace. Compressing O₂ at 900° C. is considered undesirable due to the significant material constraints noted above. Cooling the O₂ down then compressing it is another option, but such an approach will decrease the energy efficiency.

Thus, it is an object of the invention to inject oxygen from an ITM into a high temperature oxygen consuming process at relatively high recoveries without requiring compression of the oxygen. It is another object of the invention to inject oxygen from an ITM into a high temperature oxygen consuming process at relatively high recoveries without being restricted by the relatively limited selection of materials that can withstand high temperature oxygen-rich environments. It is yet another object of the invention to improve the efficiency of ITMs integrated with high temperature oxygen consuming processes.

SUMMARY

There is disclosed a method for injecting low pressure oxygen from an ion transport membrane into an ambient or super ambient pressure oxygen-consuming process, comprising the following steps. A super ambient pressure, oxygen-containing feed gas is fed to a first ion transport membrane to produce a sub-ambient pressure first permeate stream essentially consisting of oxygen and a first non-permeate stream essentially consisting of oxygen-deficient feed gas, the ion transport membrane comprising a material that is a hybrid electron/O²⁻ anion hybrid conductor. A high velocity gas is injected into the oxygen-consuming process from an interior of an inner tube, the high velocity gas having a velocity of at least 80 m/s. The sub-ambient pressure first permeate stream is injected into the oxygen consuming process form an annular space in between the inner tube and an outer tube concentrically disposed around the inner tube, the first permeate stream being sucked from the annular space by the relative vacuum created by expansion of the high velocity gas from the inner tube, the sub ambient pressure first permeate stream having a pressure of at least 8000 Pascal.

There is also provided a system for consuming oxygen that is received at low pressure from an ion transport membrane, comprising: a reactor adapted for consuming oxygen; a first ion transport membrane comprising a material that is a hybrid electron/O²⁻ anion hybrid conductor, the first ion transport membrane having an inlet, a first permeate stream outlet and a first non-permeate stream outlet; a source of a gas; and an oxygen injection device comprising an outer tube concentrically disposed around an inner tube. The inner tube has an inlet and outlet, an annular space in between the inner and outlet tubes having an inlet and outlet. The inlet of the inner tube is in fluid communication with the gas source, the inlet of the annular space is in fluid communication with the first permeate stream outlet, and the outlets of the inner tube and the annular space are in fluid communication with an interior of the reactor.

Either of or both of the method and system may include one or more of the following aspects:

-   -   the first permeate stream is not compressed before it is         injected into the oxygen-consuming process.     -   compressed air is fed to a second ion transport membrane to         produce a super ambient pressure second permeate stream         essentially consisting of oxygen and a super ambient pressure         second non-permeate stream essentially consisting of         oxygen-deficient air, wherein the oxygen-containing feed gas fed         to the first ion transport membrane is the second non-permeate         stream and the second ion transport membrane comprises a         material that is a hybrid electron/O²⁻ anion hybrid conductor.     -   the high velocity gas is the second permeate stream.     -   the oxygen-consuming process is an oxy-combustion furnace.     -   the inner and outer tubes are part of a burner that also feeds a         fuel into oxy-combustion furnace where it reacts with the first         permeate stream and the high velocity gas.     -   the oxygen-consuming process is an oxy-combustion furnace.     -   the feed gas is compressed air.     -   the high velocity gas comprises a flue gas that is recovered         from the oxy-combustion furnace.     -   the oxygen-consuming process is a combustion space of a boiler,         an industrial melting furnace, an electric arc furnace, a blast         furnace, or a partial oxidation reactor.     -   the oxygen-consuming process is an oxy-combustion furnace         producing flue gas.     -   the feed gas is compressed air that has been pre-heated through         heat exchange with the flue gas.     -   there is no compressor in fluid communication between the first         permeate stream outlet and the outer tube inlet.     -   the method or system further comprises:         -   a compressor having an air inlet; and         -   a compressed air outlet and a second ion transport membrane             comprising a material that is a hybrid electron/O²⁻ anion             hybrid conductor, the second ion transport membrane having             an inlet, a second permeate stream outlet and a second             non-permeate stream outlet, the second ion transport             membrane being adapted to permeate oxygen from a feed gas             that is fed to the inlet of the second ion transport             membrane, the non-permeate portion of the feed gas fed to             the inlet of the second ion transport membrane being             channelled to the second non-permeate stream outlet, the             permeated oxygen from the second ion transport membrane             being channelled to the second permeate stream outlet,             wherein:             -   the compressed air outlet is in fluid communication with                 the inlet of the second ion transport membrane;             -   the inlet of the first ion transport membrane is in                 fluid communication with the second non-permeate stream                 outlet; and             -   the gas source is the second permeate stream outlet.     -   the inner and outer tubes are part of a burner that is adapted         to feed a fuel into the oxy-combustion furnace where it reacts         with oxygen from the first permeate outlet that is injected from         the outlet of the annular space and oxygen from the second         permeate outlet that is injected from the outlet of the inner         tube.     -   the method or system further comprises a compressor, wherein:         -   an outlet of the compressor is in fluid communication with             the inlet of the first ion transport membrane;             -   the reactor is an oxy-combustion furnace; and             -   the gas source is compressed flue gas that is recovered                 from the oxy-combustion furnace.     -   the reactor is a combustion space of a boiler, a furnace, an         aluminum furnace, a cement kiln, an electric arc furnace, a         blast furnace, or a partial oxidation reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

FIG. 1 is a schematic of the invention with one ITM.

FIG. 2 is a schematic of the invention with two ITMs.

FIG. 3 is a CFD simulation of an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In this invention, sub ambient pressure oxygen that is permeated from an ion transport membrane is injected into an oxygen-consuming process from an oxygen injection device. The oxygen injection device comprises an outer tube concentrically disposed around an inner tube. The outlet of the inner tube and an outlet of an annular space in between the inner and outer tubes feed into an interior of a reactor in which the oxygen-consuming process takes place. A high velocity gas is injected into the reactor from the inner tube. Expansion of the high velocity gas at the outlet of the inner tube causes oxygen to be sucked from the annular space and, hence, sucked from the ion transport membrane.

The reactor containing the oxygen-consuming process is not limited. Typical types of reactors include oxy-combustion furnaces, oxy-combustion boilers, aluminum furnaces, cement kilns, electric arc furnaces having oxygen lances or oxy-combustion burners, industrial melting furnaces, and blast furnaces. The industrial melting furnace is typically a furnace in which glass, metal, or vitrifiable material such as a ceramic or frit.

The ion transport membrane is made of a material that includes a densified separation layer made of a hybrid electron/O²⁻ anion hybrid conductor. The densified separation layer is otherwise gas-tight. Such materials are well known and their details need not be duplicated herein.

An oxygen-containing feed gas (that is fed to an inlet of the ion transport membrane) is similarly not limited. Typically, the feed gas is compressed air, oxygen-deficient air, or an oxygen-containing gas derived from a high temperature, industrial process such as a glass furnace or blast furnace. At least some of the oxygen from the oxygen-containing feed gas permeates through the membrane and exits the membrane at a permeate outlet. The non-permeate portion of the oxygen-containing feed gas (now termed oxygen-deficient feed gas) exits the membrane at a non-permeate outlet. The feed gas is at a temperature high enough to maintain the temperature of the hybrid O²⁻ anion and electron conductor material so that oxygen may permeate across the membrane. Typically, the feed gas is at a temperature of about 900° C. The feed gas is also at a pressure suitably high to generate a driving force across the membrane that drives permeation of oxygen across the membrane. Typically the feed gas is at a pressure of about 16 bar.

The permeate from the membrane is at sub ambient pressure. Rather than compress the permeate in order to inject the permeate into the reactor, it is sucked into the reactor by the creation of a low pressure region adjacent the outlet of the inner tube and the outlet of the annular space that results from the expansion of the high velocity gas at the outlet of the inner tube. In this manner, oxygen that would otherwise not be able to be injected into the reactor (or injected only if it was compressed) may be injected into the reactor. As a result, higher recoveries of oxygen from the feed gas are realized. The gas pressure of the permeate should be 8000 Pascal or higher. If the pressure of the permeate is too low, it will not be able to be sucked into the reactor via the annular space.

The high velocity gas is also not limited. Typical examples include oxygen, flue gas, gaseous fuel, particulate solid fuel fluidized with a conveying gas such as air, or other industrial gas derived from a high temperature, industrial process such as a blast furnace or a partial oxidation reactor/gasifier. The high velocity gas is injected from the inner tube at a velocity sufficient to cause the oxygen to be sucked from the annular space. Typically, the velocity is at least 80 m/s or about 130-140 m/s.

The oxygen injection device may extend through a wall of the reactor so that the downstream ends of the inner and outer tubes are disposed within the reactor or their downstream ends may be flush with a wall of the reactor. The inner diameter of the outer pipe should only be a few mm larger than the outer diameter of the inner pipe in order to create the low pressure region at the outlet of the annular space. If the gap between the inner and outer pipes is too large, a high pressure zone will appear adjacent the inner surface of the outer pipe and a low pressure zone appear adjacent the outer surface of the inner pipe. In such a situation, the flue gas will recirculate at the interface of the oxygen injection device and the wall of the reactor into which it extends and the oxygen in the annular space will not be sucked into the reactor. Because the annular space is limited by the gap, the mass flow rate of oxygen sucked into the reactor is similarly limited. Therefore, a plurality of the oxygen injection devices might be necessary when a relatively large mass flow rate of oxygen needs to be sucked into the reactor from the combined annular spaces.

The suction rate (the mass flow rate of the oxygen sucked from the annular space divided by the mass flow rate of the high velocity gas) is dependent upon the velocity of the high velocity gas in the inner pipe and also upon the thickness of the gap between the inner and outer pipes. The suction rate increases when the velocity of the high velocity gas in the inner pipe increases. If the velocity of high velocity gas in the inner pipe is relatively low, the inner diameter of the outer pipe should be reduced in order to keep the same suction ratio in the gases from the outer pipe. In one embodiment, the device has seven pipe-in-pipe structures. HP O₂ flows at high velocity (130-140 m/s) in the inner pipe of each structure. O₂ at sub-atmosphere of ITM system connected to the outer pipes. As the HP O₂ flush out of the inner pipe at high speed, a negative pressure is created at the joint area of the outer pipe and furnace wall, and thus the HT/LP O₂ can be sucked into the flow stream.

The oxygen injection device can be used for a wide variety of purposes. It can be used as a burner or lance whereby the high velocity gas is oxygen. It can instead be used as a gas mixer for a high pressure gas (the high velocity gas) and a low pressure gas (the oxygen permeate at sub ambient pressure).

In one embodiment and as best shown in FIG. 1, there is only one ion transport membrane 1 (the first ion transport membrane) 1. The feed gas 3 is either compressed air or an oxygen-containing gas at super ambient pressure that is derived from a high temperature industrial process. Oxygen permeates across the first ion transport membrane 1 and exits as a first permeate stream 5 at a first permeate stream outlet. The portion of the feed gas 3 that does not permeate across the first ion transport membrane 1 exits as a first non-permeate stream 7 at a first non-permeate stream outlet. Optionally, the first non-permeate stream 7 may be used as the high velocity gas 9 if it is at a sufficiently high pressure, in which case the first non-permeate outlet is the source of the high velocity gas 9. The high velocity gas 9 is injected from the inner tube 11 and into an interior of the reactor (not shown) where the oxygen-consuming process occurs. The first permeate stream 5 is injected from an annular space 13 between the inner tube 11 and outer tube 15.

In another embodiment and as best illustrated in FIG. 2, there are two ion transport membranes 21, 22 in series. Compressed air 23 from the outlet of a compressor (not shown) is fed to the inlet of one of the ion transport membranes (the second ion transport membrane 22). Oxygen permeates across the second membrane 22 and exits as a second permeate stream 24 at a second permeate stream outlet. The second permeate outlet is in fluid communication with the inlet of the inner tube 25 so that the stream of second permeate (which is at super ambient pressure) is the high velocity gas. The remaining portion of the air (which has not permeated across the second membrane 22) exits the second membrane 22 as a second non-permeate stream 26 at a second non-permeate stream outlet. The second non-permeate 26 is oxygen-deficient air. The second non-permeate 26 (which is also at super ambient pressure) is fed to the inlet of the other ion transport membranes (the first ion transport membrane 21). Oxygen from the second non-permeate permeates 26 across the first membrane 21 and exits as a first permeate stream 27 from a first permeate stream outlet. The first permeate stream outlet is in fluid communication with an inlet of the annular space 28 of the oxygen injection device so that the first permeate stream 27 is sucked from the first membrane 21 and the annular space 28 and injected into the reactor from the outlet of the annular space 28. The remaining portion of the second non-permeate stream (which has not permeated across the first membrane 21) exits the first membrane 21 as a first non-permeate stream 29 at a first non-permeate stream outlet. The first non-permeate stream 29 ordinarily is quite low in oxygen and may be used for any purpose requiring a low oxygen or high nitrogen gas.

Prophetic Examples

CFD (Computational fluid dynamics) simulations have been conducted to calculation the amount of HT/LP O2 that can be sucked in by the HT/HP O₂ flow stream by a device having seven pipe-in-pipe structures. The flow rates of the O₂ through the inner pipes and outer pipes, the inlet velocity of the O₂ in the inner pipes, the pressure of the LP O₂, and the resultant suction ratios are listed in Table 1. The suction ratio by this design is pretty high, ranging from 15% to 56.4% depending on the pressure of the LP O₂. Table 2 shows the O₂ suction ratio when the inner oxygen flow velocity is varied. As seen in Table 2, the O₂ suction ratio increases if increasing the O₂ flow velocity. FIG. 3 shows a simulation with seven pipe-in-pipe oxygen injectors. Thus, the CFD simulation proves the efficiency of the novel design.

TABLE 1 CFD simulations of O₂ suction ratio with different inner pipe pressure Pressure of O₂ flow rate Inlet LP O₂ O₂ flow rate of the inner velocity of (relative of the outer Suction pipe inner pipe to 1 atm) pipes Ratio Case (kg/s) (m/s) (Pascal) (kg/s) (%) 1 0.14 (0.02 × 7) 136 0 0.079 56.4 2 0.14 (0.02 × 7) 136 −1000 0.047 33.6 3 0.14 (0.02 × 7) 136 −1500 0.032 22.9 4 0.14 (0.02 × 7) 136 −2000 0.021 15.0

TABLE 2 CFD simulations of O2 suction ratio with different inner oxygen flow velocity Inlet O₂ flow rate velocity Pressure of O₂ flow rate of the inner of inner LP O₂ (relative of the outer Suction pipe pipe to 1 atm) pipes Ratio Case (kg/s) (m/s) (Pascal) (kg/s) (%) 2 0.14 136 −1000 0.047 33.6 (0.02 × 7) 5 0.10 97 −1000 0.016 16.0 (0.014286 × 7) 6 0.08 78 −1000 0 0 (0.011428 × 7)

Preferred processes and apparatus for practicing the present invention have been described. It will be understood and readily apparent to the skilled artisan that many changes and modifications may be made to the above-described embodiments without departing from the spirit and the scope of the present invention. The foregoing is illustrative only and that other embodiments of the integrated processes and apparatus may be employed without departing from the true scope of the invention defined in the following claims. 

What is claimed is:
 1. A method for injecting low pressure oxygen from an ion transport membrane into an ambient or super ambient pressure oxygen-consuming process, comprising the steps of: feeding a super ambient pressure, oxygen-containing feed gas to a first ion transport membrane to produce a sub-ambient pressure first permeate stream essentially consisting of oxygen and a first non-permeate stream essentially consisting of oxygen-deficient feed gas, the ion transport membrane comprising a material that is a hybrid electron/O²⁻ anion hybrid conductor; injecting a high velocity gas into the oxygen-consuming process from an interior of an inner tube, the high velocity gas having a velocity of at least 80 m/s; and injecting the sub-ambient pressure first permeate stream into the oxygen consuming process form an annular space in between the inner tube and an outer tube concentrically disposed around the inner tube, the first permeate stream being sucked from the annular space by the relative vacuum created by expansion of the high velocity gas from the inner tube, the sub ambient pressure first permeate stream having a pressure of at least 8000 Pascal.
 2. The method of claim 1, wherein the first permeate stream is not compressed before it is injected into the oxygen-consuming process.
 3. The method of claim 1, further comprising the step of feeding compressed air to a second ion transport membrane to produce a super ambient pressure second permeate stream essentially consisting of oxygen and a super ambient pressure second non-permeate stream essentially consisting of oxygen-deficient air, wherein the oxygen-containing feed gas fed to the first ion transport membrane is the second non-permeate stream and the second ion transport membrane comprises a material that is a hybrid electron/O²⁻ anion hybrid conductor.
 4. The method of claim 3, wherein the high velocity gas is the second permeate stream.
 5. The method of claim 4, wherein: the oxygen-consuming process is an oxy-combustion furnace; and the inner and outer tubes are part of a burner that also feeds a fuel into oxy-combustion furnace where it reacts with the first permeate stream and the high velocity gas.
 6. The method of claim 1, wherein: the oxygen-consuming process is an oxy-combustion furnace; the feed gas is compressed air; and the high velocity gas comprises a flue gas that is recovered from the oxy-combustion furnace.
 7. The method of claim 1, wherein the oxygen-consuming process is a combustion space of a boiler, an industrial melting furnace, an electric arc furnace, a blast furnace, or a partial oxidation reactor.
 8. The method of claim 1, wherein: the oxygen-consuming process is an oxy-combustion furnace producing flue gas; and the feed gas is compressed air that has been pre-heated through heat exchange with the flue gas.
 9. A system for consuming oxygen that is received at low pressure from an ion transport membrane, comprising: a reactor adapted for consuming oxygen; a first ion transport membrane comprising a material that is a hybrid electron/O²⁻ anion hybrid conductor, the first ion transport membrane having an inlet, a first permeate stream outlet and a first non-permeate stream outlet; a source of a gas; an oxygen injection device comprising an outer tube concentrically disposed around an inner tube, inner tube having an inlet and outlet, an annular space in between the inner and outlet tubes having an inlet and outlet, wherein the inlet of the inner tube is in fluid communication with the gas source, the inlet of the annular space is in fluid communication with the first permeate stream outlet, and the outlets of the inner tube and the annular space are in fluid communication with an interior of the reactor.
 10. The system of claim 9, wherein there is no compressor in fluid communication between the first permeate stream outlet and the outer tube inlet.
 11. The system of claim 9, further comprising: a compressor having an air inlet; and a compressed air outlet and a second ion transport membrane comprising a material that is a hybrid electron/O²⁻ anion hybrid conductor, the second ion transport membrane having an inlet, a second permeate stream outlet and a second non-permeate stream outlet, the second ion transport membrane being adapted to permeate oxygen from a feed gas that is fed to the inlet of the second ion transport membrane, the non-permeate portion of the feed gas fed to the inlet of the second ion transport membrane being channelled to the second non-permeate stream outlet, the permeated oxygen from the second ion transport membrane being channelled to the second permeate stream outlet, wherein: the compressed air outlet is in fluid communication with the inlet of the second ion transport membrane; the inlet of the first ion transport membrane is in fluid communication with the second non-permeate stream outlet; and the gas source is the second permeate stream outlet.
 12. The system of claim 11, wherein: the reactor is an oxy-combustion furnace; and the inner and outer tubes are part of a burner that is adapted to feed a fuel into the oxy-combustion furnace where it reacts with oxygen from the first permeate outlet that is injected from the outlet of the annular space and oxygen from the second permeate outlet that is injected from the outlet of the inner tube.
 13. The system of claim 9, further comprising a compressor, wherein: an outlet of the compressor is in fluid communication with the inlet of the first ion transport membrane; the reactor is an oxy-combustion furnace; and the gas source is compressed flue gas that is recovered from the oxy-combustion furnace.
 14. The system of claim 9, wherein the reactor is a combustion space of a boiler, a furnace, an aluminum furnace, a cement kiln, an electric arc furnace, a blast furnace, or a partial oxidation reactor. 